"You move to Florida, you play golf, you go to the beach, and you get on your wife's nerves," he says. "I decided pretty quickly I had to do something else."

For Mr. Smith, that "something else" turned out to be not a weekly bridge game or a model-airplane hobby, but a Ph.D. in American history. For the next several years, he chipped away at the required coursework, archival research, and finally, the grandfather of all academic projects: a book-length dissertation.

The effort paid off in August, when, at the age of 87, he received his doctorate from Florida International University, becoming the oldest graduate in the institution's history.

Mr. Smith isn't particularly concerned with making history—he simply enjoys studying it. That, and not the chance to break a record, he says, is what compelled him to spend more than three years piecing together the first contemporary biography of John Sherman, a 19th-century political figure—U.S. senator from Ohio, secretary of state and of the treasury, chief author of the Sherman Anti-Trust Act—and brother of the General William Tecumseh Sherman.

For Darden A. Pyron, Mr. Smith's dissertation adviser, his student's age is irrelevant. "The very first conversation I had with him, I said, 'I'm not going to make any allowances for you,'" says Mr. Pyron, a professor of history. "I told him I'd treat him like everyone else on one condition: that he promise not to die on me. And, bless him, he didn't."

That sense of discipline suited Mr. Smith just fine. He had spent his working life as the co-owner of a clothing business, and during World War II he served for three years on the crew of a B-24 in Europe. He completed his undergraduate degree in business at the University of Pennsylvania's Wharton School on the GI Bill. And he and his wife raised three children. So the work required for a graduate degree in history, he says, didn't faze him.

That does not mean, however, that the Ph.D. wasn't an enormous undertaking. He and his wife of 34 years, Zenaida, logged thousands of miles driving to archives in Maine, Ohio, and Washington. For three years, he says, he wrote and rewrote the chapters of his dissertation, scrambling like any other grad student to meet the demands of his adviser.

"I would send him a draft and he would say, 'No, no, that's not good,'" says Mr. Smith. "Then he would scribble all over it and send it back to me to fix."

The tough love worked. Mr. Pyron, who is only 69, says he was pleased with the finished product and is even considering collaborating with Mr. Smith on a book about the Sherman brothers.

When they were working together on the dissertation, Mr. Pyron says, he was so focused on treating his octogenarian pupil like any other student that he says he briefly lost sight of how remarkable the situation was. That changed when Mr. Smith's name was called at graduation. As professor and student walked to the podium, Mr. Pyron recalls, the crowd erupted in cheers.

"All of these students—22 and 23 years old—were running over, giving him high fives, saying, 'You go, Richard!' It was an absolutely extraordinary moment."